I believe that the digital pin logic is disconnected from the pin when the pin is in analog mode. Otherwise the digital logic could be biased to intermediate voltages that would cause excessive current consumption.
Probably quicker to actually try it than try to analyze the datasheet "functional" diagrams...
Hmm. If you have all the voltages above the threshold, you could probably leave the pin in digital mode EXCEPT when you actually want to read the value. But note that reconfiguring the pin for analog and waiting for an A2D conversion in a pin change ISR would be ... more code than you should put in an ISR.